The development of polymeric materials with tailored surface properties plays an important role in today's society. Essential all devices and carriers contain different materials that have to be compatible with their surroundings. In addition, there is a need to develop chemistry that is based on renewable resources. Polysaccharides are a natural and renewable resource and a desirable raw material for sustainable chemistry applications. Chemical modifications of polysaccharides are often an important step to change its chemistry or structure in order to design properties needed for specific applications.[1,2] Esterification and etherification are among the most commonly used derivatizations of polysaccharides. There is much use of, and many reports on, efficient and homogenous derivatization of dissolved polysaccharides, but less on solid polysaccharides, such as cellulose. There are different technically viable approaches for cellulose modifications using, for example, acid chlorides, anhydrides and heavy metal based catalyst or nucleophilic substitutions. However, direct, inexpensive, technically simple, environmentally friendly and modular modifications of solid carbohydrates are of great interest to many industries utilizing natural fibers, but it is a challenging task due to the low reactivity of the solid surface of native cellulose and polysaccharide-based materials.[3] So called “Click” chemistry,[5] (copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition between azides and terminal alkynes)[6] have been applied to polysaccharides and allow for chemoselective and highly modular route to cellulose modifications.[7,8] The reaction of a thiol with an un-activated double bond has been used in various applications to crosslink polymers and has recently emerged as a new thiol-ene based “click” chemistry coupling reaction providing for chemo-selective bio-conjugations and polymerizations.[9-11] The thiol-ene “click” reaction does not require the need for a metal catalyst as compared with for example the copper(I)-mediated azide/alkyne click chemistry. Thiol-ene coupling also benefits from that it can be activated both thermally or photochemically and, depending on substrates, performed without solvents allowing for green and efficient reaction conditions.[12]
This invention provides the first example of the environmentally benign heterogeneous modification of polysaccharide-based materials in its native solid state by thiol-ene “click chemistry”. This “organoclick” methodology is highly modular and completely metal-free.